Percussors have been utilized as therapeutic devices to stimulate expectoration of mucus from the lungs. By stimulating the areas of the body adjacent to the thoracic cavity, mucus that lines the alveolar sacs of the lungs can be loosened and expectorated. The pressure within the alveolar sacs between inspiration and expiration is normally at atmospheric pressure. To expire, it is only necessary to create a positive pressure within the thoracic cavity that surrounds the lung thereby increasing the pressure within the alveolar sacs which results in deflation of the lungs or expiration. To inspire, the reverse occurs and a negative pressure is introduced into the thoracic cavity to cause the alveolar sacs to expand thus lowering the pressure within the alveolar sacs to draw air into the lungs. The action of a percussor on the outside of the thoracic cavity is sufficient to cause an undulation of the pressure within the thoracic cavity. This undulation is a rapid succession of impulses to the external walls of the thoracic cavity causing the pressure within the thoracic cavity to alternate between a slight negative and a slight positive pressure. This pressure variation is in turn relayed to the alveolar sacs which are interconnected by bronchioles such that a localized undulation to one section of the lungs is transferred or averaged out to the remaining alveoli. Since the percussor operates at a rate many times that of normal breathing, each of the alveolar sacs is in a sense resonated at the frequency of the percussor. This undulating action has proven to be helpful to patients suffering respiratory diseases by clearing up and reducing the amount of mucus that lines the inner walls of the alveoli.
There have been numerous types of percussors in the prior art such as the mechanically operated strobe percussor that consists of a reciprocating arm with a soft pad to produce a thumping on the chest. The motor for this mechanical percussor is contained in a hand unit, and as such, both increases the weight of the unit and the hazard that the patient's hair may be drawn into the motor. Since some patients can require many hours of use at one particular time, these types of percussors have proven impractical in that they must be held by hand as they are moved to different areas proximate to the thoracic cavity.
A pneumatic percussor which alleviates the cumbersome type of hand unit has been disclosed in U.S. Pat. No. 3,955,563 and illustrates a rubber suction cup that is attached to the end of a piston which is reciprocated in a sealed air cylinder. A control valve is operable to allow air to enter the cylinder thus extending the piston. The piston is retracted when the air supply is removed by closing the valve and a spring is operable to return the piston to a resting position. An oscillator is utilized to switch the valve on and off thereby increasing the pressure within the cylinder at the oscillator rate to provide a variable stroke rate per second. This type of percussor, although utilizing a pneumatic control, essentially results in the same type of movement that was present with the mechanical percussors.
It is desirable to have a percussor that is both lightweight with a variable stroke rate and yet provide a more gentle rhythmic motion for percussion therewith. The prior art devices fail to take into account the operator that handles the percussor since this may affect the absolute pressure that is applied to the thoracic cavity due to the fact that these percussors do not provide for any lateral dissemination of the forces therein.